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{{short description|Infection caused by pathogens that take advantage of an opportunity not normally available}}
{{Infobox medical condition (new)
{{Infobox medical condition (new)
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| image = Chest X-ray in influenza and Haemophilus influenzae - annotated.jpg
| image = Chest X-ray in influenza and Haemophilus influenzae - annotated.jpg
| caption = [[Chest radiograph|Chest X-ray]] of a patient who first had [[influenza]] and then developed ''[[Haemophilus influenzae]]'' pneumonia, presumably opportunistic
| caption = [[Chest radiograph|Chest X-ray]] of a patient who first had [[influenza]] and then developed ''[[Haemophilus influenzae]]'' pneumonia, presumably opportunistic
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An '''opportunistic infection''' is an [[infection]] caused by [[pathogen]]s ([[bacteria]], [[fungus|fungi]], [[Parasitism|parasites]] or [[virus]]es) that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a [[weakened immune system]] (as can occur in [[AIDS|acquired immunodeficiency syndrome]] or when being treated with [[immunosuppressive drug]]s, as in [[Treatment of cancer|cancer treatment]]),<ref name=":1">{{cite book | vauthors = Justiz Vaillant AA, Qurie A | chapter = Immunodeficiency |date=2021 | chapter-url= http://www.ncbi.nlm.nih.gov/books/NBK500027/ | title = StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29763203 |access-date=2021-03-09 }}</ref> an altered [[microbiome]] (such as a disruption in [[Gut flora|gut microbiota]]), or breached [[Integumentary system|integumentary]] barriers (as in [[penetrating trauma]]). Many of these pathogens do not necessarily cause disease in a healthy host that has a non-compromised immune system, and can, in some cases, act as [[Commensalism|commensals]] until the balance of the immune system is disrupted.<ref name=":2">{{cite journal | vauthors = Schroeder MR, Stephens DS | title = Macrolide Resistance in ''Streptococcus pneumoniae'' | journal = Frontiers in Cellular and Infection Microbiology | volume = 6 | pages = 98 | date = 2016-09-21 | pmid = 27709102 | pmc = 5030221 | doi = 10.3389/fcimb.2016.00098 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Achermann Y, Goldstein EJ, Coenye T, Shirtliff ME | title = Propionibacterium acnes: from commensal to opportunistic biofilm-associated implant pathogen | journal = Clinical Microbiology Reviews | volume = 27 | issue = 3 | pages = 419–40 | date = July 2014 | pmid = 24982315 | pmc = 4135900 | doi = 10.1128/CMR.00092-13 }}</ref> Opportunistic infections can also be attributed to pathogens which cause mild illness in healthy individuals but lead to more serious illness when given the opportunity to take advantage of an immunocompromised host.<ref>{{cite journal | vauthors = Caballero MT, Polack FP | title = Respiratory syncytial virus is an "opportunistic" killer | journal = Pediatric Pulmonology | volume = 53 | issue = 5 | pages = 664–667 | date = May 2018 | pmid = 29461021 | pmc = 5947624 | doi = 10.1002/ppul.23963 }}</ref>
An '''opportunistic infection''' is an [[infection]] caused by [[pathogen]]s ([[bacteria]], [[virus]]es, [[fungus|fungi]], or [[protozoa]]) that take advantage of an opportunity not normally available, such as a host with a [[immunodeficiency|weakened immune system]], an altered [[microbiota]] (such as a disrupted [[gut flora|gut microbiota]]), or breached [[integumentary system|integumentary]] barriers. Many of these pathogens do not cause disease in a healthy host that has a normal immune system. However, a compromised immune system, which is seriously debilitated and has lowered resistance to infection, a [[penetrating trauma|penetrating injury]], or a lack of competition from normal [[commensalism|commensals]] presents an opportunity for the pathogen to infect.

== Types of infections==
== Types of opportunistic infections ==
{{Further|Immunodeficiency}}
{{Further|Immunodeficiency}}


A wide variety of pathogens are involved in opportunistic infection and can cause a similarly wide range in pathologies. A partial list of opportunistic pathogens and their associated presentations includes:
A partial listing of opportunistic organisms includes:


=== Bacteria ===
* ''[[Aspergillus]]'' sp.
* ''[[Clostridioides difficile]]'' (formerly known as ''Clostridium difficile'') is a species of bacteria that is known to cause gastrointestinal infection and is typically associated with the [[Hospital-acquired infection|hospital setting]].<ref>{{cite journal | vauthors = Czepiel J, Dróżdż M, Pituch H, Kuijper EJ, Perucki W, Mielimonka A, Goldman S, Wultańska D, Garlicki A, Biesiada G | display-authors = 6 | title = Clostridium difficile infection: review | journal = European Journal of Clinical Microbiology & Infectious Diseases | volume = 38 | issue = 7 | pages = 1211–1221 | date = July 2019 | pmid = 30945014 | pmc = 6570665 | doi = 10.1007/s10096-019-03539-6 }}</ref><ref>{{cite journal | vauthors = Guh AY, Kutty PK | title = Clostridioides difficile Infection | journal = Annals of Internal Medicine | volume = 169 | issue = 7 | pages = ITC49–ITC64 | date = October 2018 | pmid = 30285209 | pmc = 6524133 | doi = 10.7326/AITC201810020 }}</ref>
* ''[[Candida albicans]]''
* ''[[Legionella pneumophila]]'' is a bacterium that causes [[Legionnaires' disease|Legionnaire's disease]], a [[Respiratory tract infection|respiratory infection]].<ref>{{cite journal | vauthors = Chahin A, Opal SM | title = Severe Pneumonia Caused by Legionella pneumophila: Differential Diagnosis and Therapeutic Considerations | journal = Infectious Disease Clinics of North America | volume = 31 | issue = 1 | pages = 111–121 | date = March 2017 | pmid = 28159171 | pmc = 7135102 | doi = 10.1016/j.idc.2016.10.009 }}</ref><ref>{{cite journal | vauthors = Berjeaud JM, Chevalier S, Schlusselhuber M, Portier E, Loiseau C, Aucher W, Lesouhaitier O, Verdon J | display-authors = 6 | title = Legionella pneumophila: The Paradox of a Highly Sensitive Opportunistic Waterborne Pathogen Able to Persist in the Environment | journal = Frontiers in Microbiology | volume = 7 | pages = 486 | date = 2016-04-08 | pmid = 27092135 | pmc = 4824771 | doi = 10.3389/fmicb.2016.00486 | doi-access = free }}</ref>
* ''[[Clostridium difficile (bacteria)|Clostridium difficile]]''
* ''[[Mycobacterium avium complex]]'' (MAC) is a group of two bacteria, ''M. avium'' and ''M. intracellulare'', that typically co-infect, leading to a lung infection called [[mycobacterium avium-intracellulare infection]].<ref>{{cite journal | vauthors = Falkinham JO | title = ''Mycobacterium avium'' complex: Adherence as a way of life | journal = AIMS Microbiology | volume = 4 | issue = 3 | pages = 428–438 | date = 2018 | pmid = 31294225 | pmc = 6604937 | doi = 10.3934/microbiol.2018.3.428 }}</ref><ref>{{cite journal | vauthors = Pan SW, Shu CC, Feng JY, Su WJ | title = Treatment for Mycobacterium avium complex lung disease | journal = Journal of the Formosan Medical Association = Taiwan Yi Zhi | volume = 119 | pages = S67–S75 | date = June 2020 | issue = Suppl 1 | pmid = 32446754 | doi = 10.1016/j.jfma.2020.05.006 | doi-access = free }}</ref>
* ''[[Coccidioides immitis]]''
* ''[[Mycobacterium tuberculosis]]'' is a species of bacteria that causes [[tuberculosis]], a respiratory infection.<ref>{{cite journal | vauthors = Gordon SV, Parish T | title = Microbe Profile: Mycobacterium tuberculosis: Humanity's deadly microbial foe | journal = Microbiology | volume = 164 | issue = 4 | pages = 437–439 | date = April 2018 | pmid = 29465344 | doi = 10.1099/mic.0.000601 | doi-access = free }}</ref>
* ''[[Cryptococcus neoformans]]''
* ''[[Pseudomonas aeruginosa]]'' is a bacterium that can cause respiratory infections. It is frequently associated with [[cystic fibrosis]] and hospital-acquired infections.<ref>{{cite journal | vauthors = Pang Z, Raudonis R, Glick BR, Lin TJ, Cheng Z | title = Antibiotic resistance in Pseudomonas aeruginosa: mechanisms and alternative therapeutic strategies | journal = Biotechnology Advances | volume = 37 | issue = 1 | pages = 177–192 | date = January–February 2019 | pmid = 30500353 | doi = 10.1016/j.biotechadv.2018.11.013 | doi-access = free }}</ref>
* ''[[Cryptosporidium]]''
* ''[[Salmonella]]'' is a [[genus]] of bacteria, known to cause gastrointestinal infections.<ref>{{cite journal | vauthors = Lamas A, Miranda JM, Regal P, Vázquez B, Franco CM, Cepeda A | title = A comprehensive review of non-enterica subspecies of Salmonella enterica | journal = Microbiological Research | volume = 206 | pages = 60–73 | date = January 2018 | pmid = 29146261 | doi = 10.1016/j.micres.2017.09.010 | doi-access = }}</ref>
* ''[[Cytomegalovirus]]''
* ''[[Staphylococcus aureus]]'' is a bacterium known to cause skin infections and [[sepsis]], among other pathologies. Notably, ''S. aureus'' has evolved several [[Drug resistance|drug-resistant]] strains, including [[Methicillin-resistant Staphylococcus aureus|MRSA]].<ref>{{cite journal | vauthors = Jenul C, Horswill AR | title = Regulation of ''Staphylococcus aureus'' Virulence | journal = Microbiology Spectrum | volume = 7 | issue = 2 | date = April 2019 | pmid = 30953424 | pmc = 6452892 | doi = 10.1128/microbiolspec.GPP3-0031-2018 }}</ref><ref>{{cite journal | vauthors = Kong C, Neoh HM, Nathan S | title = Targeting Staphylococcus aureus Toxins: A Potential form of Anti-Virulence Therapy | journal = Toxins | volume = 8 | issue = 3 | pages = 72 | date = March 2016 | pmid = 26999200 | pmc = 4810217 | doi = 10.3390/toxins8030072 | doi-access = free }}</ref>
* ''[[Geomyces destructans]]'' (bats)
* ''[[Streptococcus pneumoniae]]'' is a bacterium that causes respiratory infections.<ref name=":2" />
* ''[[Histoplasma capsulatum]]''
* ''[[Streptococcus pyogenes]]'' (also known as group A ''Streptococcus'') is a bacterium that can cause a variety of pathologies, including [[impetigo]] and [[Streptococcal pharyngitis|strep throat]], as well as other, more serious, illnesses.<ref>{{cite journal | vauthors = Jespersen MG, Lacey JA, Tong SY, Davies MR | title = Global genomic epidemiology of Streptococcus pyogenes | journal = Infection, Genetics and Evolution | volume = 86 | pages = 104609 | date = December 2020 | pmid = 33147506 | doi = 10.1016/j.meegid.2020.104609 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Brouwer S, Barnett TC, Rivera-Hernandez T, Rohde M, Walker MJ | title = Streptococcus pyogenes adhesion and colonization | journal = FEBS Letters | volume = 590 | issue = 21 | pages = 3739–3757 | date = November 2016 | pmid = 27312939 | doi = 10.1002/1873-3468.12254 | hdl = 10033/619157 | s2cid = 205213711 | hdl-access = free }}</ref>
* ''[[Isospora belli]]''

* ''[[JC virus|Polyomavirus JC polyomavirus]]'', the virus that causes [[Progressive multifocal leukoencephalopathy]].
=== Fungi ===
* ''[[Kaposi's Sarcoma]] caused by [[Human herpesvirus 8]] (HHV8)'', also called Kaposi's sarcoma-associated herpesvirus (KSHV)
* ''[[Aspergillus]]'' is a fungus, commonly associated with respiratory infection.<ref>{{cite journal | vauthors = Latgé JP, Chamilos G | title = Aspergillus fumigatus and Aspergillosis in 2019 | journal = Clinical Microbiology Reviews | volume = 33 | issue = 1 | pages = e00140–18, /cmr/33/1/CMR.00140–18.atom | date = December 2019 | pmid = 31722890 | pmc = 6860006 | doi = 10.1128/CMR.00140-18 }}</ref><ref name=":3">{{cite journal | vauthors = José RJ, Periselneris JN, Brown JS | title = Opportunistic bacterial, viral and fungal infections of the lung | journal = Medicine | volume = 48 | issue = 6 | pages = 366–372 | date = June 2020 | pmid = 32390758 | pmc = 7206443 | doi = 10.1016/j.mpmed.2020.03.006 }}</ref>
* ''[[Legionellosis|Legionnaires' Disease (Legionella pneumophila)]]''
* ''[[Candida albicans]]'' is a species of fungus that is associated with [[Oral candidiasis|oral thrush]] and gastrointestinal infection.<ref>{{cite journal | vauthors = Akpan A, Morgan R | title = Oral candidiasis | journal = Postgraduate Medical Journal | volume = 78 | issue = 922 | pages = 455–9 | date = August 2002 | pmid = 12185216 | pmc = 1742467 | doi = 10.1136/pmj.78.922.455 }}</ref><ref>{{cite journal | vauthors = Erdogan A, Rao SS | title = Small intestinal fungal overgrowth | journal = Current Gastroenterology Reports | volume = 17 | issue = 4 | pages = 16 | date = April 2015 | pmid = 25786900 | doi = 10.1007/s11894-015-0436-2 | s2cid = 3098136 }}</ref>
* ''[[Microsporidium]]''
* ''[[Coccidioides immitis]]'' is a fungus known for causing [[coccidioidomycosis]], more commonly known as Valley Fever.<ref>{{cite journal | vauthors = Mu A, Shein TT, Jayachandran P, Paul S | title = Immune Reconstitution Inflammatory Syndrome in Patients with AIDS and Disseminated Coccidioidomycosis: A Case Series and Review of the Literature | journal = Journal of the International Association of Providers of AIDS Care | volume = 16 | issue = 6 | pages = 540–545 | date = 2017-09-14 | pmid = 28911256 | doi = 10.1177/2325957417729751 | doi-access = free }}</ref>
* ''[[Mycobacterium avium complex]] (MAC) (Nontuberculosis Mycobacterium)''
* ''[[Cryptococcus neoformans]]'' is a fungus that causes [[cryptococcosis]], which can lead to pulmonary infection as well as nervous system infections, like [[meningitis]].<ref>{{cite journal | vauthors = Kwon-Chung KJ, Fraser JA, Doering TL, Wang Z, Janbon G, Idnurm A, Bahn YS | title = Cryptococcus neoformans and Cryptococcus gattii, the etiologic agents of cryptococcosis | journal = Cold Spring Harbor Perspectives in Medicine | volume = 4 | issue = 7 | pages = a019760 | date = July 2014 | pmid = 24985132 | pmc = 4066639 | doi = 10.1101/cshperspect.a019760 }}</ref><ref>{{cite journal | vauthors = Maziarz EK, Perfect JR | title = Cryptococcosis | journal = Infectious Disease Clinics of North America | volume = 30 | issue = 1 | pages = 179–206 | date = March 2016 | pmid = 26897067 | pmc = 5808417 | doi = 10.1016/j.idc.2015.10.006 }}</ref>
* ''[[Mycobacterium tuberculosis]]''
* ''[[Histoplasma capsulatum]]'' is a species of fungus known to cause [[histoplasmosis]], which can present with an array of symptoms, but often involves respiratory infection.<ref>{{cite journal | vauthors = Horwath MC, Fecher RA, Deepe GS | title = Histoplasma capsulatum, lung infection and immunity | journal = Future Microbiology | volume = 10 | issue = 6 | pages = 967–75 | date = 2015-06-10 | pmid = 26059620 | pmc = 4478585 | doi = 10.2217/fmb.15.25 }}</ref><ref>{{cite journal | vauthors = Mittal J, Ponce MG, Gendlina I, Nosanchuk JD | title = Histoplasma Capsulatum: Mechanisms for Pathogenesis | journal = Current Topics in Microbiology and Immunology | volume = 422 | pages = 157–191 | date = 2018 | pmid = 30043340 | pmc = 7212190 | doi = 10.1007/82_2018_114 | publisher = Springer International Publishing | isbn = 978-3-030-30236-8 | place = Cham | veditors = Rodrigues ML }}</ref>
* [[Pneumocystis pneumonia|''Pneumocystis jirovecii'']], previously known as [[Pneumocystis carinii|''Pneumocystis carinii'' f. ''hominis'']]
* ''[[Pseudogymnoascus destructans]]'' (formerly known as ''Geomyces destructans'') is a fungus that causes [[white-nose syndrome]] in [[bat]]s.<ref>{{cite journal | vauthors = Seyedmousavi S, Bosco SM, de Hoog S, Ebel F, Elad D, Gomes RR, Jacobsen ID, Jensen HE, Martel A, Mignon B, Pasmans F, Piecková E, Rodrigues AM, Singh K, Vicente VA, Wibbelt G, Wiederhold NP, Guillot J | display-authors = 6 | title = Fungal infections in animals: a patchwork of different situations | journal = Medical Mycology | volume = 56 | issue = suppl_1 | pages = 165–187 | date = April 2018 | pmid = 29538732 | pmc = 6251577 | doi = 10.1093/mmy/myx104 }}</ref>
* ''[[Pseudomonas aeruginosa]]''
* ''[[Microsporidia]]'' is a group of fungi that infect species across the [[Animal|animal kingdom]], one species of which can cause [[microsporidiosis]] in immunocompromised human hosts.<ref>{{cite journal | vauthors = Stentiford GD, Becnel JJ, Weiss LM, Keeling PJ, Didier ES, Bjornson S, Freeman MA, Brown MJ, Roesel K, Sokolova Y, Snowden KF, Solter L | display-authors = 6 | title = Microsporidia - Emergent Pathogens in the Global Food Chain | journal = Trends in Parasitology | volume = 32 | issue = 4 | pages = 336–348 | date = April 2016 | pmid = 26796229 | pmc = 4818719 | doi = 10.1016/j.pt.2015.12.004 }}</ref>
* ''[[Salmonella]]''
* ''[[Pneumocystis jirovecii]]'' (formerly known as ''Pneumocystis carinii'') is a fungus that causes [[pneumocystis pneumonia]], a respiratory infection.<ref>{{cite journal | vauthors = Sokulska M, Kicia M, Wesołowska M, Hendrich AB | title = Pneumocystis jirovecii--from a commensal to pathogen: clinical and diagnostic review | journal = Parasitology Research | volume = 114 | issue = 10 | pages = 3577–85 | date = October 2015 | pmid = 26281787 | pmc = 4562001 | doi = 10.1007/s00436-015-4678-6 }}</ref>
* ''[[Staphylococcus aureus]]''

* ''[[Streptococcus pneumoniae]]''
=== Parasites ===
* ''[[Streptococcus pyogenes]]''
* ''[[Cryptosporidium]]'' is a [[protozoa]]n that infects the [[gastrointestinal tract]].<ref>{{cite journal | vauthors = Gerace E, Lo Presti VD, Biondo C | title = ''Cryptosporidium'' Infection: Epidemiology, Pathogenesis, and Differential Diagnosis | journal = European Journal of Microbiology & Immunology | volume = 9 | issue = 4 | pages = 119–123 | date = December 2019 | pmid = 31934363 | pmc = 6945992 | doi = 10.1556/1886.2019.00019 }}</ref>
* ''[[Toxoplasma gondii]]''
* ''[[Toxoplasma gondii]]'' is a protozoan, known for causing [[toxoplasmosis]].<ref>{{cite journal | vauthors = Mendez OA, Koshy AA | title = Toxoplasma gondii: Entry, association, and physiological influence on the central nervous system | journal = PLOS Pathogens | volume = 13 | issue = 7 | pages = e1006351 | date = July 2017 | pmid = 28727854 | pmc = 5519211 | doi = 10.1371/journal.ppat.1006351 | veditors = Gubbels MJ | doi-access = free }}</ref><ref>{{cite journal | vauthors = Hunter CA, Sibley LD | title = Modulation of innate immunity by Toxoplasma gondii virulence effectors | journal = Nature Reviews. Microbiology | volume = 10 | issue = 11 | pages = 766–78 | date = November 2012 | pmid = 23070557 | pmc = 3689224 | doi = 10.1038/nrmicro2858 }}</ref>

=== Viruses ===
* ''[[Cytomegalovirus]]'' is a family of opportunistic viruses, most frequently associated with respiratory infection.<ref name=":3" /><ref>{{cite journal | vauthors = Fonseca Brito L, Brune W, Stahl FR | title = Cytomegalovirus (CMV) Pneumonitis: Cell Tropism, Inflammation, and Immunity | journal = International Journal of Molecular Sciences | volume = 20 | issue = 16 | pages = 3865 | date = August 2019 | pmid = 31398860 | pmc = 6719013 | doi = 10.3390/ijms20163865 | doi-access = free }}</ref>
* ''[[Human polyomavirus 2]]'' (also known as JC virus) is known to cause [[progressive multifocal leukoencephalopathy]] (PML).<ref>{{cite journal | vauthors = Bohra C, Sokol L, Dalia S | title = Progressive Multifocal Leukoencephalopathy and Monoclonal Antibodies: A Review | journal = Cancer Control | volume = 24 | issue = 4 | pages = 1073274817729901 | date = 2017-11-01 | pmid = 28975841 | pmc = 5937251 | doi = 10.1177/1073274817729901 }}</ref><ref>{{cite journal | vauthors = Kartau M, Sipilä JO, Auvinen E, Palomäki M, Verkkoniemi-Ahola A | title = Progressive Multifocal Leukoencephalopathy: Current Insights | journal = Degenerative Neurological and Neuromuscular Disease | volume = 9 | pages = 109–121 | date = 2019-12-02 | pmid = 31819703 | pmc = 6896915 | doi = 10.2147/DNND.S203405 | doi-access = free }}</ref>
* ''[[Kaposi's sarcoma-associated herpesvirus|Human herpesvirus 8]]'' (also known as Kaposi sarcoma-associated herpesvirus) is a virus associated with [[Kaposi's sarcoma|Kaposi sarcoma]], a type of cancer.<ref>{{cite journal | vauthors = Radu O, Pantanowitz L | title = Kaposi sarcoma | journal = Archives of Pathology & Laboratory Medicine | volume = 137 | issue = 2 | pages = 289–94 | date = February 2013 | pmid = 23368874 | doi = 10.5858/arpa.2012-0101-RS | doi-access = }}</ref><ref>{{cite journal | vauthors = Cesarman E, Damania B, Krown SE, Martin J, Bower M, Whitby D | title = Kaposi sarcoma | journal = Nature Reviews. Disease Primers | volume = 5 | issue = 1 | pages = 9 | date = January 2019 | pmid = 30705286 | pmc = 6685213 | doi = 10.1038/s41572-019-0060-9 }}</ref>


== Causes ==
== Causes ==
[[Immunodeficiency]] or [[immunosuppression]] can be caused by:
[[Immunodeficiency]] or [[immunosuppression]] are characterized by the absence of or disruption in components of the immune system, leading to lower-than-normal levels of immune function and immunity against pathogens.<ref name=":1" /> They can be caused by a variety of factors, including:
* [[Malnutrition]]
* [[Malnutrition]]
* [[Fatigue (medical)|Fatigue]]
* [[Fatigue (medical)|Fatigue]]
Line 62: Line 70:
* [[genetics|Genetic]] predisposition
* [[genetics|Genetic]] predisposition
* [[Skin]] damage
* [[Skin]] damage
* [[Antibiotic]] treatment leading to disruption of the physiological [[microbiome]], thus allowing some microorganisms to outcompete others and become [[pathogenic]] (e.g. disruption of [[intestinal flora|intestinal microbiota]] may lead to ''[[Clostridium difficile colitis|Clostridium difficile]]'' infection
* [[Antibiotic]] treatment leading to disruption of the physiological [[microbiome]], thus allowing some microorganisms to outcompete others and become [[pathogenic]] (e.g. disruption of [[intestinal flora|intestinal microbiota]] may lead to ''[[Clostridium difficile colitis|Clostridium difficile]]'' infection)
* Medical procedures
* Medical procedures
* Pregnancy {{further|Susceptibility and severity of infections in pregnancy}}
* Pregnancy {{further|Susceptibility and severity of infections in pregnancy}}
* [[Ageing|Aging]]
* [[Ageing|Aging]]
* [[Leukopenia]] (i.e. [[neutropenia]] and [[lymphocytopenia]])
* [[Leukopenia]] (i.e. [[neutropenia]] and [[lymphocytopenia]])
* Burns


The lack of or the disruption of [[List of microbiota species of the lower reproductive tract of women|normal vaginal microbiota]] allows the proliferation of [[List of bacterial vaginosis microbiota|opportunistic microorganisms]] and will cause the opportunistic infection - [[bacterial vaginosis]].<ref name="AfricaNel2014">{{cite journal|last1=Africa|first1=Charlene|last2=Nel|first2=Janske|last3=Stemmet|first3=Megan|title=Anaerobes and Bacterial Vaginosis in Pregnancy: Virulence Factors Contributing to Vaginal Colonisation|journal=International Journal of Environmental Research and Public Health|volume=11|issue=7|year=2014|pages=6979–7000|issn=1660-4601|doi=10.3390/ijerph110706979|pmid=25014248|pmc=4113856}}</ref><ref name=Mastro2013>{{cite journal|last1=Mastromarino|first1=Paola|last2=Vitali|first2=Beatrice|last3=Mosca|first3=Luciana|title=Bacterial vaginosis: a review on clinical trials with probiotics|url=http://www.newmicrobiologica.org/PUB/allegati_pdf/2013/3/229.pdf|journal=New Microbiologica|date=2013|volume=36|issue=3|pages=229–238|pmid=23912864}}</ref><ref>{{cite journal|last1=Mastromarino|first1=Paola|last2=Vitali|first2=Beatrice|last3=Mosca|first3=Luciana|title=Bacterial vaginosis: a review on clinical trials with probiotics|url=http://www.newmicrobiologica.org/PUB/allegati_pdf/2013/3/229.pdf|journal=New Microbiologica|date=2013|volume=36|issue=3|pages=229–238|pmid=23912864}}</ref><ref>{{cite journal|last1=Knoester|first1=M.|last2=Lashley|first2=L. E. E. L. O.|last3=Wessels|first3=E.|last4=Oepkes|first4=D.|last5=Kuijper|first5=E. J.|title=First Report of Atopobium vaginae Bacteremia with Fetal Loss after Chorionic Villus Sampling|journal=Journal of Clinical Microbiology|volume=49|issue=4|year=2011|pages=1684–1686|issn=0095-1137|doi=10.1128/JCM.01655-10|pmid=21289141|pmc=3122803}}</ref>
The lack of or the disruption of [[List of microbiota species of the lower reproductive tract of women|normal vaginal microbiota]] allows the proliferation of [[List of bacterial vaginosis microbiota|opportunistic microorganisms]] and will cause the opportunistic infection [[bacterial vaginosis]].<ref name="AfricaNel2014">{{cite journal | vauthors = Africa CW, Nel J, Stemmet M | title = Anaerobes and bacterial vaginosis in pregnancy: virulence factors contributing to vaginal colonisation | journal = International Journal of Environmental Research and Public Health | volume = 11 | issue = 7 | pages = 6979–7000 | date = July 2014 | pmid = 25014248 | pmc = 4113856 | doi = 10.3390/ijerph110706979 | doi-access = free }}</ref><ref name=Mastro2013>{{cite journal | vauthors = Mastromarino P, Vitali B, Mosca L | title = Bacterial vaginosis: a review on clinical trials with probiotics | journal = The New Microbiologica | volume = 36 | issue = 3 | pages = 229–38 | date = July 2013 | pmid = 23912864 | url = http://www.newmicrobiologica.org/PUB/allegati_pdf/2013/3/229.pdf }}</ref><ref>{{cite journal | vauthors = Mastromarino P, Vitali B, Mosca L | title = Bacterial vaginosis: a review on clinical trials with probiotics | journal = The New Microbiologica | volume = 36 | issue = 3 | pages = 229–38 | date = July 2013 | pmid = 23912864 | url = http://www.newmicrobiologica.org/PUB/allegati_pdf/2013/3/229.pdf }}</ref><ref>{{cite journal | vauthors = Knoester M, Lashley LE, Wessels E, Oepkes D, Kuijper EJ | title = First report of Atopobium vaginae bacteremia with fetal loss after chorionic villus sampling | journal = Journal of Clinical Microbiology | volume = 49 | issue = 4 | pages = 1684–6 | date = April 2011 | pmid = 21289141 | pmc = 3122803 | doi = 10.1128/JCM.01655-10 }}</ref>

== Opportunistic Infection and HIV/AIDS ==
HIV is a virus that targets [[T cell]]s of the [[immune system]] and, as a result, HIV infection can lead to progressively worsening immunodeficiency, a condition ideal for the development of opportunistic infection.<ref>{{cite journal | vauthors = Doitsh G, Greene WC | title = Dissecting How CD4 T Cells Are Lost During HIV Infection | journal = Cell Host & Microbe | volume = 19 | issue = 3 | pages = 280–91 | date = March 2016 | pmid = 26962940 | pmc = 4835240 | doi = 10.1016/j.chom.2016.02.012 }}</ref><ref>{{cite journal | vauthors = Fenwick C, Joo V, Jacquier P, Noto A, Banga R, Perreau M, Pantaleo G | title = T-cell exhaustion in HIV infection | journal = Immunological Reviews | volume = 292 | issue = 1 | pages = 149–163 | date = November 2019 | pmid = 31883174 | pmc = 7003858 | doi = 10.1111/imr.12823 }}</ref> Because of this, respiratory and central nervous system opportunistic infections, including tuberculosis and meningitis, respectively, are associated with later-stage HIV infection, as are numerous other infectious pathologies.<ref>{{cite journal | vauthors = Bruchfeld J, Correia-Neves M, Källenius G | title = Tuberculosis and HIV Coinfection | journal = Cold Spring Harbor Perspectives in Medicine | volume = 5 | issue = 7 | pages = a017871 | date = February 2015 | pmid = 25722472 | pmc = 4484961 | doi = 10.1101/cshperspect.a017871 }}</ref><ref>{{cite journal | vauthors = Tenforde MW, Shapiro AE, Rouse B, Jarvis JN, Li T, Eshun-Wilson I, Ford N | title = Treatment for HIV-associated cryptococcal meningitis | journal = The Cochrane Database of Systematic Reviews | volume = 2018 | pages = CD005647 | date = July 2018 | issue = 7 | pmid = 30045416 | pmc = 6513250 | doi = 10.1002/14651858.CD005647.pub3 | collaboration = Cochrane Infectious Diseases Group }}</ref> Kaposi's sarcoma, a virally-associated cancer, has higher incidence rates in HIV-positive patients than in the general population.<ref>{{cite journal | vauthors = Rees CA, Keating EM, Lukolyo H, Danysh HE, Scheurer ME, Mehta PS, Lubega J, Slone JS | display-authors = 6 | title = Mapping the Epidemiology of Kaposi Sarcoma and Non-Hodgkin Lymphoma Among Children in Sub-Saharan Africa: A Review | journal = Pediatric Blood & Cancer | volume = 63 | issue = 8 | pages = 1325–31 | date = August 2016 | pmid = 27082516 | pmc = 7340190 | doi = 10.1002/pbc.26021 }}</ref> As immune function declines and HIV-infection progresses to AIDS, individuals are at an increased risk of opportunistic infections that their immune systems are no longer capable of responding properly to. Because of this, opportunistic infections are a leading cause of HIV/AIDS-related deaths.<ref>{{cite book | vauthors = Sadiq U, Shrestha U, Guzman M | chapter = Prevention Of Opportunistic Infections In HIV |date=2021 | chapter-url = http://www.ncbi.nlm.nih.gov/books/NBK513345/| title = StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30020717 |access-date=2021-03-09 }}</ref>


== Prevention ==
== Prevention ==
Since opportunistic infections can cause severe disease, much emphasis is placed on measures to prevent infection. Such a strategy usually includes restoration of the immune system as soon as possible, avoiding exposures to infectious agents, and using antimicrobial medications ("prophylactic medications") directed against specific infections.<ref>{{cite book|author=David Schlossberg|title=Clinical Infectious Disease|url=https://books.google.com/books?id=meFwBwAAQBAJ&pg=PA688|date=2015-04-23|publisher=Cambridge University Press|isbn=978-1-107-03891-2|pages=688–}}</ref>
Since opportunistic infections can cause severe disease, much emphasis is placed on measures to prevent infection. Such a strategy usually includes restoration of the immune system as soon as possible, avoiding exposures to infectious agents, and using antimicrobial medications ("prophylactic medications") directed against specific infections.<ref>{{cite book| vauthors = Schlossberg D |title=Clinical Infectious Disease|url=https://books.google.com/books?id=meFwBwAAQBAJ&pg=PA688|date=2015-04-23|publisher=Cambridge University Press|isbn=978-1-107-03891-2|pages=688–}}</ref>


=== Restoration of immune system ===
=== Restoration of immune system ===
* In patients with HIV, starting [[Management of HIV/AIDS|antiretroviral therapy]] is especially important for restoration of the immune system and reducing the incidence rate of opportunistic infections<ref>{{Cite journal|title = AIDS-related opportunistic illnesses occurring after initiation of potent antiretroviral therapy: the Swiss HIV Cohort Study|url = https://www.ncbi.nlm.nih.gov/pubmed?term=10605973|journal = JAMA|date = Dec 15, 1999|access-date = 2015-05-09|issn = 0098-7484|pmid = 10605973|pages = 2220–2226|volume = 282|issue = 23|first = B.|last = Ledergerber|first2 = M.|last2 = Egger|first3 = V.|last3 = Erard|first4 = R.|last4 = Weber|first5 = B.|last5 = Hirschel|first6 = H.|last6 = Furrer|first7 = M.|last7 = Battegay|first8 = P.|last8 = Vernazza|first9 = E.|last9 = Bernasconi|doi=10.1001/jama.282.23.2220}}</ref><ref>{{Cite journal|title = HIV-associated opportunistic infections--going, going, but not gone: the continued need for prevention and treatment guidelines|url = https://www.ncbi.nlm.nih.gov/pubmed?term=19191648|journal = Clinical Infectious Diseases|date = Mar 1, 2009|access-date = 2015-05-09|issn = 1537-6591|pmid = 19191648|pages = 609–611|volume = 48|issue = 5|doi = 10.1086/596756|first = John T.|last = Brooks|first2 = Jonathan E.|last2 = Kaplan|first3 = King K.|last3 = Holmes|first4 = Constance|last4 = Benson|first5 = Alice|last5 = Pau|first6 = Henry|last6 = Masur}}</ref>
* In patients with HIV, starting [[Management of HIV/AIDS|antiretroviral therapy]] is especially important for restoration of the immune system and reducing the incidence rate of opportunistic infections<ref>{{cite journal | vauthors = Ledergerber B, Egger M, Erard V, Weber R, Hirschel B, Furrer H, Battegay M, Vernazza P, Bernasconi E, Opravil M, Kaufmann D, Sudre P, Francioli P, Telenti A | display-authors = 6 | title = AIDS-related opportunistic illnesses occurring after initiation of potent antiretroviral therapy: the Swiss HIV Cohort Study | journal = JAMA | volume = 282 | issue = 23 | pages = 2220–6 | date = December 1999 | pmid = 10605973 | doi = 10.1001/jama.282.23.2220 }}</ref><ref>{{cite journal | vauthors = Brooks JT, Kaplan JE, Holmes KK, Benson C, Pau A, Masur H | title = HIV-associated opportunistic infections--going, going, but not gone: the continued need for prevention and treatment guidelines | journal = Clinical Infectious Diseases | volume = 48 | issue = 5 | pages = 609–11 | date = March 2009 | pmid = 19191648 | doi = 10.1086/596756 | s2cid = 39742988 | doi-access = }}</ref>
* In patients undergoing chemotherapy, completion of and recovery from treatment is the primary method for immune system restoration. In a select subset of high risk patients, [[Granulocyte colony-stimulating factor|granulocyte colony stimulating factors (G-CSF)]] can be used to aid immune system recovery.<ref>{{Cite journal|title = Clinical practice guideline for the use of antimicrobial agents in neutropenic patients with cancer: 2010 update by the infectious diseases society of america|url = https://www.ncbi.nlm.nih.gov/pubmed?term=21258094|journal = Clinical Infectious Diseases|date = Feb 15, 2011|access-date = 2015-05-09|issn = 1537-6591|pmid = 21258094|pages = e56–93|volume = 52|issue = 4|doi = 10.1093/cid/cir073|first = Alison G.|last = Freifeld|first2 = Eric J.|last2 = Bow|first3 = Kent A.|last3 = Sepkowitz|first4 = Michael J.|last4 = Boeckh|first5 = James I.|last5 = Ito|first6 = Craig A.|last6 = Mullen|first7 = Issam I.|last7 = Raad|first8 = Kenneth V.|last8 = Rolston|first9 = Jo-Anne H.|last9 = Young}}</ref><ref>{{Cite journal|title = 2006 update of recommendations for the use of white blood cell growth factors: an evidence-based clinical practice guideline|url = https://www.ncbi.nlm.nih.gov/pubmed?term=16682719|journal = Journal of Clinical Oncology|date = Jul 1, 2006|access-date = 2015-05-09|issn = 1527-7755|pmid = 16682719|pages = 3187–3205|volume = 24|issue = 19|doi = 10.1200/JCO.2006.06.4451|first = Thomas J.|last = Smith|first2 = James|last2 = Khatcheressian|first3 = Gary H.|last3 = Lyman|first4 = Howard|last4 = Ozer|first5 = James O.|last5 = Armitage|first6 = Lodovico|last6 = Balducci|first7 = Charles L.|last7 = Bennett|first8 = Scott B.|last8 = Cantor|first9 = Jeffrey|last9 = Crawford}}</ref>
* In patients undergoing chemotherapy, completion of and recovery from treatment is the primary method for immune system restoration. In a select subset of high risk patients, [[Granulocyte colony-stimulating factor|granulocyte colony stimulating factors]] (G-CSF) can be used to aid immune system recovery.<ref>{{cite journal | vauthors = Freifeld AG, Bow EJ, Sepkowitz KA, Boeckh MJ, Ito JI, Mullen CA, Raad II, Rolston KV, Young JA, Wingard JR | display-authors = 6 | title = Clinical practice guideline for the use of antimicrobial agents in neutropenic patients with cancer: 2010 update by the infectious diseases society of america | journal = Clinical Infectious Diseases | volume = 52 | issue = 4 | pages = e56-93 | date = February 2011 | pmid = 21258094 | doi = 10.1093/cid/cir073 | doi-access = }}</ref><ref>{{cite journal | vauthors = Smith TJ, Khatcheressian J, Lyman GH, Ozer H, Armitage JO, Balducci L, Bennett CL, Cantor SB, Crawford J, Cross SJ, Demetri G, Desch CE, Pizzo PA, Schiffer CA, Schwartzberg L, Somerfield MR, Somlo G, Wade JC, Wade JL, Winn RJ, Wozniak AJ, Wolff AC | display-authors = 6 | title = 2006 update of recommendations for the use of white blood cell growth factors: an evidence-based clinical practice guideline | journal = Journal of Clinical Oncology | volume = 24 | issue = 19 | pages = 3187–205 | date = July 2006 | pmid = 16682719 | doi = 10.1200/JCO.2006.06.4451 | doi-access = free }}</ref>


=== Infectious exposures to avoid ===
=== Avoidance of infectious exposure ===
The following may be avoided as a preventative measure to reduce the risk of infection:
* Eating undercooked meat or eggs, unpasteurized dairy products or juices.
* Potential sources of tuberculosis (high-risk healthcare facilities, regions with high rates of tuberculosis, patients with known tuberculosis).
* Any oral exposure to feces.<ref name=":0">{{Cite web|date=26 May 2020|title=Guidelines for the prevention and treatment of opportunistic infections in adults and adolescents with HIV: recommendations from the Centers for Disease Control and Prevention, the National Institutes of Health, and the HIV Medicine Association of the Infectious Diseases Society of America|url=https://clinicalinfo.hiv.gov/sites/default/files/guidelines/documents/Adult_OI.pdf|access-date=28 November 2020}}</ref>
* Contact with farm animals, especially those with diarrhea: source of ''[[Toxoplasma gondii]]'', ''[[Cryptosporidium parvum]].''
* Cat feces (e.g. cat litter): source of ''[[Toxoplasma gondii]]'', [[Bartonella|''Bartonella'' spp]].
* Cat feces (e.g. cat litter): source of ''[[Toxoplasma gondii]]'', [[Bartonella|''Bartonella'' spp]].
* Soil/dust in areas where there is known [[histoplasmosis]], [[coccidioidomycosis]].
* Eating undercooked meat or eggs, unpasteurized dairy products or juices
* Reptiles, chicks, and ducklings are a common source of ''[[Salmonella]]''.
* Potential sources of tuberculosis (high risk healthcare facilities, regions with high rates of tuberculosis, patients with known tuberculosis)
* Unprotected sexual intercourse with individuals with known [[sexually transmitted infection]]s.
* Contact with farm animals, especially those with diarrhea: source of ''[[Toxoplasma gondii]]'', ''[[Cryptosporidium parvum]]''
* Soil/dust in areas where there is known [[histoplasmosis]], [[Coccidioidomycosis|coccidiomycosis]]
* Reptiles, chicks, ducklings: source of [[Salmonella|''Salmonella'' spp]].
* Unprotected sexual intercourse with individuals with known [[sexually transmitted infection]]s.
*Any oral exposure to feces.<ref>{{Cite web|url = http://aidsinfo.nih.gov/guidelines/html/4/adult-and-adolescent-oi-prevention-and-treatment-guidelines/362/appendix-a--preventing-exposure|title = AIDSinfo: Recommendations to Help HIV-infected Patients Avoid Exposure to, or Infection from, Opportunistic Pathogens|date = 5/7/2013|accessdate = 2015-05-09|website = |publisher = |last = |first = }}</ref>


=== Prophylactic medications ===
=== Prophylactic medications ===
Individuals at higher risk are often prescribed prophylactic medication to prevent an infection from occurring. A patient's risk level for developing an opportunistic infection is approximated using the patient's [[CD4|CD4 T-cell count]] and sometimes other markers of susceptibility. Common prophylaxis treatments include the following:<ref>{{Cite web|url = http://aidsinfo.nih.gov/contentfiles/lvguidelines/adult_oi.pdf|title = AIDSinfo: Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents|date = 2013-06-17|accessdate = 2015-05-09|website = |publisher = |last = |first = }}</ref>
Individuals at higher risk are often prescribed prophylactic medication to prevent an infection from occurring. A person's risk level for developing an opportunistic infection is approximated using the person's [[CD4|CD4 T-cell count]] and other indications. The table below provides information regarding the treatment management of common opportunistic infections.<ref name=":4">{{Cite book |last1=Dyer |first1=Mary |url=http://www.ncbi.nlm.nih.gov/books/NBK567851/ |title=Comprehensive Primary Care for Adults With HIV |last2=Kerr |first2=Christine |last3=McGowan |first3=Joseph P. |last4=Fine |first4=Steven M. |last5=Merrick |first5=Samuel T. |last6=Stevens |first6=Lyn C. |last7=Hoffmann |first7=Christopher J. |last8=Gonzalez |first8=Charles J. |date=2021 |publisher=Johns Hopkins University |series=New York State Department of Health AIDS Institute Clinical Guidelines |location=Baltimore (MD) |pmid=33625815}}</ref><ref name=":5">{{Cite web |title=European AIDS Clinical Society Guidelines |url=https://www.eacsociety.org/media/final2021eacsguidelinesv11.0_oct2021.pdf}}</ref><ref name=":6">{{Cite web |title=Table 2. Treatment of HIV-Associated Opportunistic Infections (Includes Recommendations for Acute Treatment and Secondary Prophylaxis/Chronic Suppressive/Maintenance Therapy) {{!}} NIH |url=https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-opportunistic-infections/treatment-hiv-associated-full |access-date=2023-02-20 |website=clinicalinfo.hiv.gov |language=en}}</ref>
{| class="wikitable"
{| class="wikitable"
!Opportunistic infections
!Infection
!Indication(s) for prophylactic medications
!When to Give Prophylaxis
!Preferred agent(s)
!Agent
!When to discontinue agent(s)
!Secondary prophylactic/maintenance agent(s)
|-
|[[Mycobacterium tuberculosis]]
|Upon diagnosis of HIV, any positive screening test, or prior medical history of Mycobacterium tuberculosis.
|
* [[Rifampicin]]
* [[Isoniazid]]
* [[Pyridoxine]]
* [[Pyrazinamide]]
* [[Ethambutol]]
|These current agents' doses/frequency will discontinue after two months. Depending on clinical presentation, maintenance agents will continue for at least four more months.
|
* Rifampicin, isoniazid, and pyridoxine
|-
|[[Pneumocystis jirovecii|Pneumocystis jiroveci]]
|[[CD4|CD4 count]] is less than 200 cells/mm<sup>3</sup> or less than 14%. The person has documented medical history of recurrent [[Oral candidiasis|oropharyngeal candidiasis]].
|
* [[Trimethoprim/sulfamethoxazole|Trimethoprim-sulfamethoxazole]]
|This current agent doses/frequency will discontinue after 21 days. Secondary prophylactic agent dose/frequency will continue until the CD4 count is above 200 cells/mm<sup>3</sup> and the HIV viral load is undetectable for at least three months while taking [[antiretroviral therapy]].
|
* Trimethoprim-sulfamethoxazole
|-
|[[Toxoplasma gondii]]
|CD4 count is less than 100 cells/mm<sup>3</sup> or less than 14%, and the person has a positive serology for Toxoplasma gondii.
|
* Trimethoprim-sulfamethoxazole
|This agent will discontinue after six weeks. Secondary prophylactic medications will continue until the CD4 count is above 200 cells/mm<sup>3</sup> and HIV viral load is undetectable for at least six months while taking antiretroviral therapy.
|
* [[Sulfadiazine]], [[pyrimethamine]], and [[folinic acid]]
|-
|[[Mycobacterium avium-intracellulare infection|Mycobacterium avium complex disease]]
|CD4 count is less than 50 cells/mm<sup>3</sup> and has a detectable viral load while taking antiretroviral therapy.
|
* [[Clarithromycin]] and ethambutol
* Rifabutin may be added depending on clinical presentation.
|These agent(s) will discontinue after 12 months only if the person does not have any symptoms that will be concerning for persistent Mycobacterium avium complex disease and their CD4 count is above 100 cells/mm<sup>3</sup>, and while their HIV viral load is undetectable for at least six months while taking antiretroviral therapy.
|N/A
|}
Alternative agents can be used instead of the preferred agents. These alternative agents may be used due to allergies, availability, or clinical presentation. The alternative agents are listed in the table below.<ref name=":4" /><ref name=":5" /><ref name=":6" />
{| class="wikitable"
!Opportunistic infections
!Alternative agent(s)
|-
|[[Mycobacterium tuberculosis]]
|
* [[Rifabutin]]
|-
|-
|[[Pneumocystis jirovecii]]
|[[Pneumocystis jirovecii|Pneumocystis jiroveci]]
|
|CD4 < 200 cells/mm3 or [[Oral candidiasis|oropharyngeal candidasis (thrush)]]
* [[Dapsone]]
|[[Trimethoprim/sulfamethoxazole|TMP-SMX]]
* [[Atovaquone]]
* [[Pentamidine]]
|-
|-
|[[Toxoplasma gondii]]
|[[Toxoplasma gondii]]
|
|CD4 < 100 cells/mm3 and positive Toxoplasma gondii IgG immunoassay
* Dapsone, pyrimethamine, and folinic acid
|[[Trimethoprim/sulfamethoxazole|TMP-SMX]]
* Atovaquone, pyrimethamine, and folinic acid
|-
|-
|[[Mycobacterium avium complex]]
|[[Mycobacterium avium-intracellulare infection|Mycobacterium avium complex disease]]
|
|CD4 < 50
|[[Azithromycin]]
* [[Azithromycin]] and ethambutol
|}
|}


==Treatment==
==Treatment==
Treatment depends on the type of opportunistic infection, but usually involves different [[antibiotic]]s.
Treatment depends on the type of opportunistic infection, but usually involves different [[antibiotic]]s.{{cn|date=June 2022}}


==Veterinary treatment==
==Veterinary treatment==
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{{clear}}
{{clear}}


==References==
== References ==
{{Reflist}}
{{Reflist}}
== External links ==
== External links ==
{{Medical resources
{{Medical resources
| DiseasesDB =
| DiseasesDB =
| ICD10 =
| ICD10 =
| ICD9 =
| ICD9 =
| ICDO =
| ICDO =
| OMIM =
| OMIM =
| MedlinePlus =
| MedlinePlus =
| eMedicineSubj =
| eMedicineSubj =
| eMedicineTopic =
| eMedicineTopic =
| MeshID = D009894
| MeshID = D009894
}}
}}
{{Concepts in infectious disease}}
[[Category:Infectious diseases]]
[[Category:Infectious diseases]]
[[Category:Immunology]]
[[Category:Immunology]]

Latest revision as of 19:26, 28 October 2024

Opportunistic infection
Chest X-ray of a patient who first had influenza and then developed Haemophilus influenzae pneumonia, presumably opportunistic
SpecialtyInfectious diseases Edit this on Wikidata

An opportunistic infection is an infection caused by pathogens (bacteria, fungi, parasites or viruses) that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune system (as can occur in acquired immunodeficiency syndrome or when being treated with immunosuppressive drugs, as in cancer treatment),[1] an altered microbiome (such as a disruption in gut microbiota), or breached integumentary barriers (as in penetrating trauma). Many of these pathogens do not necessarily cause disease in a healthy host that has a non-compromised immune system, and can, in some cases, act as commensals until the balance of the immune system is disrupted.[2][3] Opportunistic infections can also be attributed to pathogens which cause mild illness in healthy individuals but lead to more serious illness when given the opportunity to take advantage of an immunocompromised host.[4]

Types of opportunistic infections

[edit]
Further information: Immunodeficiency

A wide variety of pathogens are involved in opportunistic infection and can cause a similarly wide range in pathologies. A partial list of opportunistic pathogens and their associated presentations includes:

Bacteria

[edit]

Fungi

[edit]

Parasites

[edit]

Viruses

[edit]

Causes

[edit]

Immunodeficiency or immunosuppression are characterized by the absence of or disruption in components of the immune system, leading to lower-than-normal levels of immune function and immunity against pathogens.[1] They can be caused by a variety of factors, including:

The lack of or the disruption of normal vaginal microbiota allows the proliferation of opportunistic microorganisms and will cause the opportunistic infection bacterial vaginosis.[38][39][40][41]

Opportunistic Infection and HIV/AIDS

[edit]

HIV is a virus that targets T cells of the immune system and, as a result, HIV infection can lead to progressively worsening immunodeficiency, a condition ideal for the development of opportunistic infection.[42][43] Because of this, respiratory and central nervous system opportunistic infections, including tuberculosis and meningitis, respectively, are associated with later-stage HIV infection, as are numerous other infectious pathologies.[44][45] Kaposi's sarcoma, a virally-associated cancer, has higher incidence rates in HIV-positive patients than in the general population.[46] As immune function declines and HIV-infection progresses to AIDS, individuals are at an increased risk of opportunistic infections that their immune systems are no longer capable of responding properly to. Because of this, opportunistic infections are a leading cause of HIV/AIDS-related deaths.[47]

Prevention

[edit]

Since opportunistic infections can cause severe disease, much emphasis is placed on measures to prevent infection. Such a strategy usually includes restoration of the immune system as soon as possible, avoiding exposures to infectious agents, and using antimicrobial medications ("prophylactic medications") directed against specific infections.[48]

Restoration of immune system

[edit]
  • In patients with HIV, starting antiretroviral therapy is especially important for restoration of the immune system and reducing the incidence rate of opportunistic infections[49][50]
  • In patients undergoing chemotherapy, completion of and recovery from treatment is the primary method for immune system restoration. In a select subset of high risk patients, granulocyte colony stimulating factors (G-CSF) can be used to aid immune system recovery.[51][52]

Avoidance of infectious exposure

[edit]

The following may be avoided as a preventative measure to reduce the risk of infection:

Prophylactic medications

[edit]

Individuals at higher risk are often prescribed prophylactic medication to prevent an infection from occurring. A person's risk level for developing an opportunistic infection is approximated using the person's CD4 T-cell count and other indications. The table below provides information regarding the treatment management of common opportunistic infections.[54][55][56]

Opportunistic infections Indication(s) for prophylactic medications Preferred agent(s) When to discontinue agent(s) Secondary prophylactic/maintenance agent(s)
Mycobacterium tuberculosis Upon diagnosis of HIV, any positive screening test, or prior medical history of Mycobacterium tuberculosis. These current agents' doses/frequency will discontinue after two months. Depending on clinical presentation, maintenance agents will continue for at least four more months.
  • Rifampicin, isoniazid, and pyridoxine
Pneumocystis jiroveci CD4 count is less than 200 cells/mm3 or less than 14%. The person has documented medical history of recurrent oropharyngeal candidiasis. This current agent doses/frequency will discontinue after 21 days. Secondary prophylactic agent dose/frequency will continue until the CD4 count is above 200 cells/mm3 and the HIV viral load is undetectable for at least three months while taking antiretroviral therapy.
  • Trimethoprim-sulfamethoxazole
Toxoplasma gondii CD4 count is less than 100 cells/mm3 or less than 14%, and the person has a positive serology for Toxoplasma gondii.
  • Trimethoprim-sulfamethoxazole
 This agent will discontinue after six weeks. Secondary prophylactic medications will continue until the CD4 count is above 200 cells/mm3 and HIV viral load is undetectable for at least six months while taking antiretroviral therapy.
Mycobacterium avium complex disease CD4 count is less than 50 cells/mm3 and has a detectable viral load while taking antiretroviral therapy.
  • Clarithromycin and ethambutol
  • Rifabutin may be added depending on clinical presentation.
 These agent(s) will discontinue after 12 months only if the person does not have any symptoms that will be concerning for persistent Mycobacterium avium complex disease and their CD4 count is above 100 cells/mm3, and while their HIV viral load is undetectable for at least six months while taking antiretroviral therapy. N/A

Alternative agents can be used instead of the preferred agents. These alternative agents may be used due to allergies, availability, or clinical presentation. The alternative agents are listed in the table below.[54][55][56]

Opportunistic infections Alternative agent(s)
Mycobacterium tuberculosis
Pneumocystis jiroveci
Toxoplasma gondii
  • Dapsone, pyrimethamine, and folinic acid
  • Atovaquone, pyrimethamine, and folinic acid
Mycobacterium avium complex disease

Treatment

[edit]

Treatment depends on the type of opportunistic infection, but usually involves different antibiotics.[citation needed]

Veterinary treatment

[edit]

Opportunistic infections caused by feline leukemia virus and feline immunodeficiency virus retroviral infections can be treated with lymphocyte T-cell immunomodulator.

Wikimedia Commons has media related to Opportunistic infections.

References

[edit]
  1. ^ a b Justiz Vaillant AA, Qurie A (2021). "Immunodeficiency". StatPearls. Treasure Island (FL): StatPearls Publishing. PMID 29763203. Retrieved 2021-03-09.
  2. ^ a b Schroeder MR, Stephens DS (2016-09-21). "Macrolide Resistance in Streptococcus pneumoniae". Frontiers in Cellular and Infection Microbiology. 6: 98. doi:10.3389/fcimb.2016.00098. PMC 5030221. PMID 27709102.
  3. ^ Achermann Y, Goldstein EJ, Coenye T, Shirtliff ME (July 2014). "Propionibacterium acnes: from commensal to opportunistic biofilm-associated implant pathogen". Clinical Microbiology Reviews. 27 (3): 419–40. doi:10.1128/CMR.00092-13. PMC 4135900. PMID 24982315.
  4. ^ Caballero MT, Polack FP (May 2018). "Respiratory syncytial virus is an "opportunistic" killer". Pediatric Pulmonology. 53 (5): 664–667. doi:10.1002/ppul.23963. PMC 5947624. PMID 29461021.
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